1. Field of the Invention
This invention relates to a sheet conveying apparatus for conveying a sheet, and an image forming apparatus provided with the sheet conveying apparatus.
2. Related Background Art
Among conventional image forming apparatuses, there are image forming apparatuses in which the discharging direction of a recording medium after image fixing can be changed over to thereby effect face-down discharge and face-up discharge. Such image forming apparatuses are described, for example, in Japanese Patent Application Laid-open No. H09-278252, Japanese Patent Application Laid-open No. 2002-145504 and Japanese Patent Application Laid-open No. 2001-341919. The image forming apparatuses of include a construction as shown in Japanese Patent Application Laid-open No. H09-278252 and Japanese Patent Application Laid-open No. 2002-145504 wherein a plurality of pairs of rollers are provided downstream of a rockable guide provided downstream of a fixing device, and a construction as shown in Japanese Patent Application Laid-open No. 2001-341919 wherein only one pair of rollers are provided. An example of this construction will hereinafter be described with reference to FIGS. 11A and 11B of the accompanying drawings. In the following, description will be made of a construction in which a plurality of pairs of rollers are provided downstream of a rockable guide.
There is an image forming apparatus which effects discharge in a face-down state (hereinafter referred to as the face-down discharge) in which, as shown in FIG. 11A, a surface on which an image is formed becomes the lower side of a recording medium, and discharge in a face-up state (hereinafter referred to as the face-up discharge) in which the surface on which an image is formed becomes the upper side of the recording medium. The image forming apparatus which effects the face-down discharge and the face-up discharge has a stacking surface 109 for stacking recording mediums thereon with the image-formed surfaces thereof in the face-down state, and a tray 111 for stacking the recording mediums thereon with the image-formed surfaces thereof in the face-up state. Also, a pair of conveying rollers 106 and pairs of rollers 107 and 108 are disposed downstream of a fixing portion for effecting image fixing with respect to a recording medium conveying direction.
In case of the face-down discharge of the recording medium, the tray 111 is closed as shown in FIG. 11A. A conveying guide 110 is closed in operative association with this. The recording medium is conveyed to the pair of rollers 107 and the pair of rollers 108 while being guided by the conveying guide 110. In this process, the upper surface and lower surface of the recording medium are reversed and the recording medium is stacked on the stacking surface 109 with the image-formed surface facing down.
In case of the face-up discharge of the recording medium, the tray 111 is opened as shown in FIG. 11B. The conveying guide 110 is opened in operative association with this. As a result, the conveying guide 110 is spaced apart from the pair of conveying rollers 106 and therefore, the recording medium is conveyed without being guided by the conveying guide 110, and the recording medium is stacked on the tray 111 with the surface thereof having an image formed thereon facing up.
According to the above-described art, however, when in the face-up discharge of the recording medium, if the recording mediums are stacked with the surfaces thereof having images formed thereon facing up, there has been the following problem. In FIGS. 12A to 12C, a recording medium Pt designates the uppermost one of the recording mediums stacked on the conveying guide 110 and the tray 111. Also, a recording medium Pn denotes a recording medium conveyed from the pair of conveying rollers 106 to the conveying guide 110 and the tray 111.
Depending on the ambient environment, there is a case where as shown in FIG. 12A, the recording medium Pt is discharged with its trailing edge flexed upwardly. When the next recording medium Pn is discharged from the pair of conveying rollers 106, there is a case where as shown in FIG. 12B, the lower surface of the trailing edge of the recording medium Pt and the upper surface of the leading edge of the recording medium Pn contact with each other. When as shown in FIG. 12C, the recording medium Pn is upwardly conveyed by the conveying force of the pair of conveying rollers 106, there is the possibility that the recording medium Pn may abuts against the nip portion between the pair of discharging rollers 107, whereby the smooth discharge of the recording medium may be hindered. As the result, there is also the possibility that discharge not intended by a user may be effected or jam may occur due to the discharge of the recording medium.
Also, even in a construction wherein the pair of rollers 107 are absent and only one pair of rollers are provided on the most downstream side of a conveying path, when the trailing edge of the recording medium Pt and the recording medium Pn enter a conveying path 116, there is the possibility that the smooth discharge of the recording medium may be hampered.